Elucidation of the Transformation of Coordination Polymer Intermediates into 2D Metal–Organic Framework Films during Chemical Vapor Deposition

Chemical vapor deposition (CVD) is a rising tool to synthesize metal-organic framework (MOF) films. Despite growing interest and usage, its mechanism is less known. Especially, the identification of intermediates is crucial for understanding the growth mechanism and further controlling their structures. In this paper, we investigated the growth mechanism of 2D MOF Cu₃(C₆O₆)₂ film by CVD. We identified a novel intermediate phase: an octahedral coordination polymer that transforms into an edge-on-oriented 2D MOF. In situ grazing-incidence wide-angle X-ray scattering, X-ray absorption near-edge structure, high-resolution transmission electron microscopy, and Raman spectroscopy studies confirmed that this transformation involves the removal of pillars, leading to the formation of a square-planar 2D MOF. With the identification of intermediates, our study deepens the understanding of MOF film formation by CVD, which lays a foundation to control the structure.